An illumination unit as this type of surface light source device has been hitherto used as a display device for information equipment such as a laptop type or notebook-size type word processor, computer or the like because of its features such as lightness in weight, thin design and low power consumption. In particular, this illumination unit is attached to a transmissive type liquid crystal panel while stacked on the liquid crystal panel, so that an image displayed on the liquid crystal panel can be visible.
Furthermore, in connection with the recent propagation of liquid crystal display devices in the amusement industry, it has been demanded that the screen size of a liquid crystal panel used as this type of liquid crystal display device is increased, the brightness of the liquid crystal panel is further enhanced, and the lifetime of the liquid crystal panel is increased.
The illumination unit for illuminating light from the backside to the liquid crystal panel used for this type of liquid crystal display device is equipped with a slender lamp unit as disclosed in, for example, Japanese Laid-Open Patent Publication No. 2003-66448. In this lamp unit, rubber lamp holders for supporting a tubular light source are attached to both end portions of the light source. Furthermore, a reflection sheet for reflecting light from the light source of the lamp unit to the liquid crystal panel side is attached to the lamp unit.
Furthermore, a light guide plate through which light from the light source of the lamp unit is efficiently transmitted to the liquid crystal panel is attached to the lamp unit while one end portion of the light guide plate faces the light source and one end face thereof is brought into contact with one side surface of the lamp holder. The lamp unit is designed so that it can be detached from the illumination unit by pulling out the lamp unit from the illumination unit in the longitudinal direction to be replaced with a new one.
However, in the liquid crystal display device described above, the lamp holder attached to the one side surface of the lamp holder is brought into contact with one end face of the light guide plate. Accordingly, when the lamp unit is used for a long period of time, the light guide plate is deformed by heat from the light source of the lamp unit, and one side surface of the lamp holder sticks to the light guide plate. This sticking cannot be eliminated even when the light source is turned off to cool the lamp unit. Accordingly, there is a risk that a part of the lamp holder is damaged and thus remains in the illumination unit every time the lamp unit is replaced with a new one. Therefore, there is a problem that it is difficult to replace the lamp unit.
The present invention has been implemented in view of the foregoing problem, and has an object to provide a surface light source device, a flat type display device and a liquid crystal display device in which a light source can be easily replaced with a new one.